Methods to control force in reluctance actuators based on flux related parameters

ABSTRACT

Disclosed herein are reluctance actuators and methods for feedback control of their applied force. Embodiments of the reluctance actuators include an electromagnet positioned to deflect a metallic plate to provide a haptic output. The control of the force is provided without force sensors (sensorless control) by monitoring voltage and/or current (V/I) applied during an actuation. For a given intended force output, an electrical parameter value (flux, current, or other parameter) is read from a look up table (LUT). The LUT may store a present value of the inductance of the reluctance actuator. The feedback control may be a quasi-static control in which the LUT is updated after actuation based on the monitored V/I. The feedback control may be real-time, with a controller comparing an estimated electrical parameter value based on the measured V/I with the value from the LUT.

FIELD

The present disclosure generally relates to magnetic reluctanceactuators and methods of providing haptic output by such reluctanceactuators, and more particularly to control using measurements ofmagnetic flux, inductance, and other parameters, either before or duringactuation.

BACKGROUND

Electronic devices are commonplace in today's society. Exampleelectronic devices include cell phones, tablet computers, personaldigital assistants, and the like. These electronic devices may provide ahaptic (touch/vibration) output to provide information, responses, oralerts to a user. Examples of such haptic outputs are vibrations on acomputer trackpad or vibrations on a cellphone, among others.

Such haptic outputs can be provided by an actuator, which may take theform of an electromechanical device that deflects or otherwise moves aflexible component. For a quality user experience, the amount of forceprovided by a haptic actuator may be monitored and controlled by acontrol system. Some control systems use feedback with a directmeasurement of the output being provided. In the case of a force outputfrom a haptic actuator, the feedback would be of direct measurements ofthe force it applies. This may be done directly through use of forcesensors positioned on the component of the actuator, such as a plate,that provides the haptic output. This can require multiple forcesensors, such as strain sensors, positioned on the flexible component.

SUMMARY

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription section. This summary is not intended to identify keyfeatures or essential features of the claimed subject matter, nor is itintended to be used as an aid in determining the scope of the claimedsubject matter.

Disclosed herein are devices that include reluctance actuators, and alsomethods for the control of forces provided by such reluctance actuators.A reluctance actuator can include an electromagnet positioned near ametallic object or plate so that a current in the electromagnet (anactuation) induces a magnetic flux (or just ‘flux’) that induces a forceof attraction on the metallic object. The metallic object may be aferritic plate positioned near a mostly planar coil forming theelectromagnet. Various methods are presented for control of the forceprovided by such reluctance actuators. The methods may make use of acorrelator component, such as a look up table, that may be updated basedon feedback. The methods may use sensorless control feedback, in thatthe force output of the reluctance actuators is not measured directly,but is estimated based on electrical parameters of the reluctanceactuators related to the magnetic flux. Such electrical parameters ofthe reluctance actuators include, but are not limited to, any ofmeasurements of the current and/or voltage in the reluctance actuatorduring actuation, measurements or estimates of the magnetic flux itself,and estimates of an inductance and a resistance of the reluctanceactuator.

More specifically, described herein is a method of controlling forceapplied by a reluctance actuator. The method includes receiving anintended force output to be applied by the reluctance actuator, andobtaining from a correlator component, such as a look up table (LUT),based at least on the intended force output and a stored estimate of anelectrical parameter value of the reluctance actuator, an inputparameter to be applied to the reluctance actuator. The method includesapplying the input parameter to the reluctance actuator to cause anactuation of the reluctance actuator; obtaining at least one of ameasurement of a current or a measurement of a voltage in the reluctanceactuator during the actuation, estimating at least one of a resistanceof the reluctance actuator, an inductance of the reluctance actuator,and a magnetic flux produced by the reluctance actuator using the atleast one of the measurement of the current and the measurement of thevoltage; and updating the stored estimate of the electrical parametervalue of the reluctance actuator of the correlator component based onthe at least one estimate of the resistance of the reluctance actuator,the inductance of the reluctance actuator or the magnetic flux producedby reluctance actuator.

In additional and/or alternative embodiments, the input parameter may bea voltage value or a current value to be applied by a driver to thereluctance actuator. The methods may include updating the storedestimate of the electrical parameter value of the reluctance actuatorafter the actuation. A measurement of the magnetic flux produced by thereluctance actuator during the actuation from a magnetic flux sensorassociated with the reluctance actuator may be used as part ofestimating the inductance of the reluctance actuator.

Also described herein are haptic actuators that include a reluctanceactuator and control electronics for the reluctance actuator. Thereluctance actuator may include a metallic plate and an electromagnetpositioned adjacent to the metallic plate; the control electronics mayinclude a correlator component, such as a look up table (LUT), a drivercomponent operably linked with the electromagnet, and an estimationcomponent. The control electronics may be operable to receive a forcetrajectory, and determine an input parameter for the driver componentusing the force trajectory as an input to the correlator component. Theinput parameter may be applied to the driver component to cause anactuation of the reluctance actuator, the estimation component maymonitor at least one of a voltage or a current in the reluctanceactuator, and the correlator component may be updated based on themonitored value of at least one of the voltage and the current in thereluctance actuator.

In additional and/or alternative embodiments, the correlator componentof the haptic actuators may store an estimate of an electrical parametervalue of the reluctance actuator, and use the stored estimate of theelectrical parameter value of the reluctance actuator with the forcetrajectory to determine the input parameter for the driver component.The driver component may be a current amplifier and the input parametermay be a current value. The driver component may be a voltage amplifierand the input parameter may be a voltage value. The control electronicsmay include a controller component that provides a feedback controlinput to the driver component based on the monitored value of thecurrent in the reluctance actuator.

The control electronic components may further include a magnetic fluxestimator operable to determine an estimate of the magnetic flux in thereluctance actuator during the actuation based on the monitored valuesof the voltage and the current in the reluctance actuator and providethe estimate of the magnetic flux to the controller element.Additionally and/or alternatively, the control electronics componentsmay further include a magnetic flux sensor associated with theelectromagnet and operable to obtain a measurement of the magnetic fluxin the reluctance actuator during the actuation, and provide themeasurement of the magnetic flux to the magnetic flux estimator.

Also described herein are methods of control of a force applied by areluctance actuator that includes an electromagnet and a flexiblemetallic plate. The method includes receiving an intended force output,and determining, using a correlator component, such as a look up table(LUT), based on the intended force output and an initial value of anelectrical parameter value of the reluctance actuator, an inputparameter. The method includes receiving at a feedback controller theinput parameter and a feedback value of the electrical parameter valueof the reluctance actuator. The methods may include: applying, by thefeedback controller, an input drive value to a driver component, theinput drive value based on the input parameter and the feedback value ofthe electrical parameter value of the reluctance actuator; applying, bythe driver component, an output drive value to the electromagnet toactuate the reluctance actuator; measuring a current in the reluctanceactuator during the actuation; and using the measured current todetermine the feedback value of the electrical parameter value of thereluctance actuator. The input parameter of the electrical parameter maybe a current.

In additional and/or alternative embodiments, the input drive value is afirst input drive value, and the methods may include determining, basedon the input parameter, a second input drive value; and applying thesecond input drive value to the driver component by a feed-forwardcomponent. The methods may include measuring a voltage in the reluctanceactuator during the actuation, determining an estimated resistance andan estimated inductance of the reluctance actuator based on the measuredcurrent and voltage, and updating the LUT by replacing the initial valueof the inductance of the reluctance actuator with the estimatedinductance of the reluctance actuator.

The input value of the electrical parameter may be an input value of amagnetic flux, and the methods may further include estimating a magneticflux in the reluctance actuator during the actuation based on themeasured voltage and current in the reluctance actuator duringactuation, and using the estimated magnetic flux in the reluctanceactuator as the feedback value of the electrical parameter received atthe feedback controller. Additionally and/or alternatively, the methodsmay include receiving, from a magnetic flux sensor associated with theelectromagnet, a measurement of a magnetic flux in the reluctanceactuator during the actuation, and using the measurement of the magneticflux in the reluctance actuator as the feedback value of the electricalparameter received at the feedback controller.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the detailed description inconjunction with the accompanying drawings, wherein like referencenumerals designate like structural elements.

FIG. 1A illustrates a laptop computer with a trackpad.

FIG. 1B illustrates a tablet computer.

FIG. 2A shows a cut away view of a reluctance actuator.

FIG. 2B shows a side view of a reluctance actuator.

FIG. 3 is a block diagram of components of control systems that may beused with reluctance actuators.

FIG. 4 is a block diagram of components of a control system for areluctance actuator.

FIG. 5 is a block diagram of components of a control system that may beused with a reluctance actuator.

FIG. 6 is a block diagram of components of a control system that may beused with a reluctance actuator.

FIG. 7 is a block diagram of components of a control system that may beused with a reluctance actuator.

FIG. 8 is a flow chart of a method for controlling a reluctanceactuator.

FIG. 9 is a flow chart of a method for controlling a force applied by areluctance actuator.

The use of cross-hatching or shading in the accompanying figures isgenerally provided to clarify the boundaries between adjacent elementsand also to facilitate legibility of the figures. Accordingly, neitherthe presence nor the absence of cross-hatching or shading conveys orindicates any preference or requirement for particular materials,material properties, element proportions, element dimensions,commonalities of similarly illustrated elements, or any othercharacteristic, attribute, or property for any element illustrated inthe accompanying figures.

Additionally, it should be understood that the proportions anddimensions (either relative or absolute) of the various features andelements (and collections and groupings thereof) and the boundaries,separations, and positional relationships presented therebetween, areprovided in the accompanying figures merely to facilitate anunderstanding of the various embodiments described herein and,accordingly, may not necessarily be presented or illustrated to scale,and are not intended to indicate any preference or requirement for anillustrated embodiment to the exclusion of embodiments described withreference thereto.

DETAILED DESCRIPTION

Reference will now be made in detail to representative embodimentsillustrated in the accompanying drawings. It should be understood thatthe following descriptions are not intended to limit the embodiments toone preferred embodiment. To the contrary, it is intended to coveralternatives, modifications, and equivalents as can be included withinthe spirit and scope of the described embodiments as defined by theappended claims.

The embodiments described herein are directed to haptic output deviceshaving reluctance actuators, and to systems and methods controlling thereluctance actuators. Examples of such devices include, but are notlimited to, trackpad, buttons, switches, display screens, housings, orother haptic output surfaces of an electronic device.

The reluctance actuators described herein include an electromagnetpositioned adjacent to, or sufficiently close to, a metallic object orplate, which may be ferromagnetic, so that a magnetic field produced bythe electromagnet induces a magnetic field within the metallic object.For simplicity of exposition, hereinafter the metallic object will bepresumed to be a plate, though one skilled in the art will recognizethat the reluctance actuators can use metallic objects with othergeometries or shapes. The electromagnets are positioned so that when acurrent is induced through them, the magnetic field is directed towardthe metallic plate. Physically, the magnetic flux preferentially tendsto be contained in the metallic plate, resulting in a force applied tothe metallic plate that attracts it toward the electromagnet.

The applied force may cause the metallic plate to bend or flex. Byapplying an appropriate current pattern over time, such as a simplesinusoid or a more complex current pattern, a corresponding intendedforce output (or “force trajectory”) can be applied to the metallicplate. The resulting flexing or bending of the metallic plate can beused to induce a respective haptic (touch) output pattern. An intendedforce output or force trajectory may also be a constant value, such asto produce a divot, bump, or other deflection of a surface as a hapticoutput of a device.

The embodiments described herein include feedback methods forcontrolling the actual force output produced by a reluctance actuator.The methods include both quasi-static and real-time feedback control. Inquasi-static feedback control, adjustments of the parameters of, orinputs to, the reluctance actuator that cause its actuation (such as acurrent needed to induce the force output) are made after an actuationand a determination that adjustment is needed. In real-time feedbackcontrol, adjustments to those inputs to the reluctance actuator thatcause its actuation are adjusted continuously (or near-continuously, orat specific intervals across a period of time). A goal of both suchfeedback control methods is to ensure an actual value of an output (suchas the force applied by the reluctance actuator) equals an intended ordesired value of that output, or at least that the actual value ispracticably close to the intended or desired value.

Feedback control of a force output provided by reluctance actuators maycompensate for manufacturing variances and component drift over time andusage. A goal is to provide a consistent, uniform output force. As anexample, a trackpad of a laptop computer may provide a haptic (or touch)output in response to a certain user input, such as providing a “click”feel when the user presses to activate a program of an icon displayed onthe laptop's screen. User experience is improved if this feel isconsistent between devices and over time.

Feedback control is often implemented by directly measuring the actualvalue of the output of interest (e.g., the output that results from thecontrol). In the case that the output of interest is the force appliedto the metallic object of a reluctance actuator, direct measurement ofthe force would require force sensors, such as piezoelectric sensors,piezoresistive sensors, strain gauges, or the like, to be attached tothe metallic object. This could add complexity and cost to an associatedelectronic device.

Various embodiments described herein are directed to non-direct feedbackcontrol of a force output from a reluctance actuator. Instead ofdirectly measuring an output force, other parameters of the reluctanceactuator are measured to estimate or infer the actual output forceprovided, and to adjust operation (feedback) of the reluctance actuator.Two such parameters that can be measured or monitored are the currentand the voltage in the reluctance actuator during the actuation. Anotherparameter, which may be directly measured, is the magnetic flux. Whilethe magnetic flux may be directly measured by any of various sensors, itprovides an indirect parameter value to be used for feedback control ofthe reluctance actuator's actual output force.

As haptic outputs typically occur briefly over a limited amount of time,quasi-static feedback control may suffice. In quasi-static feedbackcontrol, adjustments are made to the reluctance actuator or its controlelectronics after an actuation.

In various embodiments disclosed herein, the control electronics for areluctance actuator include a correlator component that takes in (orreceives) at least a desired or intended force output, and provides aninput parameter (such as a voltage or current value) that is used byother control electronics to drive the reluctance actuator so as toproduce the intended force output. Such a correlator component may beimplemented, in various embodiments, as a look up table (LUT). Such aLUT may be implemented as a one-, two-, or higher dimensional table orarray (depending on the number of received inputs at the correlatorcomponent) from which the provided input parameter is read off. Such atable may be implemented as an integrated circuit comprising a memorystoring the table. Such a memory may be modifiable, as will be discussedin the families of embodiments described below. In other embodiments, acorrelator component may be implemented as: a processor or processingcomponents running software programs that calculates the inputparameter, as an application specific integrated circuit producing anoutput or signal correlated with the input parameter; or by otherelectronic circuits or components. In the embodiments to be described,the correlator component or its operations may by modifiable usingfeedback based on an observed haptic output of the haptic actuator.

The correlator component may be modifiable in order to account forvariations of the components of the reluctance actuator due tomanufacture and usage. As an example, in the case that the correlatorcomponent is a LUT, implemented as a two-dimensional (or even higherdimensional) array, the LUT may additionally receive or take in one ormore entries corresponding to properties of the reluctance actuator toprovide the input parameter.

For example, such a LUT may need the desired force output as a firstentry and an inductance value of the reluctance actuator to read out thecorresponding input parameter with which to drive the reluctanceactuator. Such a LUT would have the desired force output as a firstdimension of the 2D array, with inductance as a second dimension. Onevalue of the inductance can be stored as a present estimate (pendingfurther update) of the inductance of the reluctance actuator.

At manufacture of an electronic device, an associated correlatorcomponent may have stored estimates or values (in the case of a LUT) orsoftware operations (in the case a software-implemented correlatorcomponent) based on design characteristics. However, due tomanufacturing variances or drifts in electronic component values,further updates based on feedback control (either quasi-static orreal-time) during usage may be made.

In various embodiments, one or both of quasi-static or real-timefeedback control of the force output provided by a reluctance actuatormay make use of estimates of the inductance and/or resistance of thereluctance actuator obtained during actuation. These estimates may bebased on measurements of the current and/or voltage across thereluctance actuator during actuation. Current and voltage sensing may beimplemented as part of a driver component for the reluctance actuator.

These and other embodiments are discussed below with reference to FIGS.1A-9. However, those skilled in the art will readily appreciate that thedetailed description given herein with respect to these Figures is forexplanatory purposes only and should not be construed as limiting. Inparticular, for simplicity of explanation only, in the exemplaryembodiments now to be described, the correlator component will beassumed to be a LUT. One skilled in the art will recognize that otherimplementations of a correlator component may be used in place of theLUT.

Further, although specific electronic devices are shown in the figuresand described below, the reluctance actuators described herein may beused with various electronic devices including, but not limited to,mobile phones, personal digital assistants, a time keeping device, ahealth monitoring device, a wearable electronic device, an input device(e.g., a stylus), a desktop computer, electronic glasses, and so on.Although various electronic devices are mentioned, the reluctanceactuators and methods of their control described in the presentdisclosure may also be used in conjunction with other products andcombined with various materials.

FIG. 1A illustrates an example electronic device 100 that mayincorporate one or more reluctance actuators and associated controlmethods according to one or more embodiments of the present disclosure.The electronic device 100 in this example is a laptop computer. Theelectronic device 100 includes a display screen 102 on which visualoutput may be displayed. The electronic device 100 includes a keyboard104 by which a user 108 may enter data and/or instructions foroperations.

The electronic device 100 also includes a trackpad 106 through which theuser 108 can move a cursor, enter data, or enter commands by touch orforce applied to the trackpad 106. The trackpad 106 may include areluctance actuator to provide haptic output or feedback to the user108. Although FIGS. 1A-1B show different electronic devices 100 and 110,like reference numerals are used to designate similar components.

FIG. 1B illustrates a second example electronic device 110 that mayincorporate one or more reluctance actuators and associated controlmethods according to one or more embodiments of the present disclosure.The electronic device 110 in this example is a tablet computer. A smartphone may be another example electronic device that has an analogousconfiguration of components and may incorporate one or more reluctanceactuators and associated control methods. The electronic device 110includes a display screen 114 on which visual output may be displayed.The electronic device 110 includes two button entries 112 a and 112 b bywhich a user 116 may alter operation of the electronic device 110, suchas change volume settings, turn on/off, etc.

A user 116 may move a cursor, enter data, or enter commands by touch orforce applied to the display screen 114. The display screen 114 mayinclude one or more reluctance actuators to provide haptic output orfeedback to the user 116.

FIG. 2A shows a cutaway view of an example configuration of a reluctanceactuator 200, such as may be used with the electronic devices describedin FIGS. 1A-B, or other electronic devices. The reluctance actuator 200includes a metallic plate 204, which may be able to deflect or flex. Themetallic plate 204 is shown partially cutaway to show componentsunderneath, and may extend as a plane further over those components. Themetallic plate 204 may be positioned against or proximate to an interiorsurface of the electronic device to provide a haptic output on a surfaceof the electronic device as it flexes or deflects. Though in the exampleconfiguration of FIG. 2A the reluctance actuator includes the metallicplate 204, in other embodiments, the plate may be replaced by a disk oranother shape that can be attracted electromagnetically to anelectromagnet 210 (described in more detail below), and so cause ahaptic output as a result. The metallic plate 204 may include a ferriticmetal, such as a steel alloy, ALNICO, or alloys using nickel, cobalt, orothers so that the metallic plate is ferromagnetic.

The reluctance actuator 200 may be situated on a support surface 202 ofthe electronic device, which may be a printed circuit board, mid plate,structural support, enclosure, or the like. In some embodiments, thesupport surface 202 may be affixed on its bottom side 208 to furtherstructures within the electronic device, or may be affixed by one ormore connectors to other structures. The metallic plate 204 may besupported above the support surface 202 on supports 206, as shownfurther in FIG. 2B.

The example configuration of the reluctance actuator 200 also includesat least one electromagnet 210 situated in, under, or on the supportsurface 202. The electromagnet 210 may be configured as a mostly planarcoil of wires (shaped, for example, as a toroid or elongate ovoid), sothat its vertical dimension may be small with respect to a lateraldimension. In other embodiments other configurations may be used. Theelectromagnet 210 may have electrical contacts 212 that extend to asource of electrical power, such as a voltage source or current source,and other control electronics, as described further below. Theelectrical contacts 212 may be implemented as leads on, in, or below thesupport surface 202, which may be a printed circuit board, or as wiresextending to other electronics, or as another implementation.

The electromagnet 210 may be connected to control electronics (asdescribed below) through the electrical contacts 212. The controlelectronics can provide an alternating or other current through theelectrical contacts 212 so that the electromagnet 210 produces amagnetic flux, as described further below.

FIG. 2B shows a cross-section view of the example reluctance actuator200. The metallic plate 204 is shown supported above the support surface202 by supports 206 a and 206 b. Though only the two supports 206 a and206 b are shown, the metallic plate 204 may be supported by anothernumber of supports. In the example configuration shown, the metallicplate 204 is supported at its edges so as to be able to flex near itscenter upon actuation. However, other mounting configurations may beused, such as a cantilever configuration, in which an edge or side ofthe metallic plate 204 is free to flex upon actuation. The supports 206may be either rigid or flexible, depending on the amount and nature ofthe haptic output desired for the electronic device.

In the embodiment shown in FIG. 2B, the electromagnet 210 is shown asembedded in the support surface 202 with the electrical contacts 212extending exterior through the support surface 202. One skilled in theart will recognize that such a configuration is not necessary, as otherembodiments may have the electromagnet 210 mounted on top of the supportsurface 202, while still other embodiments may have the electromagnet210 mounted below the support surface 202.

A current flowing in the electromagnet 210 induces magnetic flux aroundits coils, as indicated by the magnetic flux lines 214 a and 214 b abovethe electromagnet 210 and their continuation 216 below the electromagnet210. In embodiments in which the metallic plate 204 is ferromagnetic,the portions of the magnetic flux lines 214 a and 214 b above theelectromagnet 210 are induced to be mostly confined to the metallicplate 204 and generate a force of attraction with the electromagnet 210that tends to reduce the gap distance 218. Flexing of the metallic plate204 under this force can be used to generate a haptic output on asurface of an electronic device. The metallic plate 204 may beferromagnetic to produce a relatively stronger deflection force in themetallic plate 204 than if it were made of a paramagnetic or diamagneticmaterial, though such materials may be used if smaller forces or flexesare preferred.

For the example reluctance actuator 200 shown, the force on the metallicplate 204 is given by F=Φ²/2μ₀n²A_(c), where n is the number ofwindings, Φ is the magnetic flux, A_(c) is the cross-sectional area, andμ₀ is the permeability of free space. The values of n and A_(c) aredetermined by design specification, though A_(c) may be subject tomanufactured variations. For the configuration of the reluctanceactuator 200 shown, this formula becomes F=μ₀n²A_(c)/2(I/g)², where I isthe current and g is the gap distance 218. This reduces to the formF=μ₀n²A_(c)/2(LI)², showing the force F in terms of the current I andthe inductance L of the actuator. One consequence is that the flux Φ isproportional to the square root of the force, or that the current I isproportional to the square root of the force divided by the inductance.These are non-linear relationships between the intended force output andthe controllable inputs to the reluctance actuator 200.

A direct measurement of the force applied by the reluctance actuator 200on its metallic plate 204 could be implemented using force sensors, suchas piezoelectric sensors, piezoresistive sensors, or another type, andwould require further wiring and control components. It some embodimentsit may be preferable to infer the applied force based on measurements ofother parameters of the actuator. Examples of such embodiments are asnow presented.

FIG. 3 is a block diagram showing components of example systems 300 thatmay be used, such as by a haptic actuator of an electronic device, tocontrol an actual output force 315 applied by the reluctance actuator312. Various embodiments described herein may use fewer or morecomponents than depicted. The particular components shown may beimplemented as single electronic or electromagnetic components, such assingle integrated circuits, or as multiple such components. In someembodiments of the example systems 300, various components and/or theiroperations may be implemented by software running on a processor orother computational electronics.

A force trajectory 302 is received as an input to the systems 300. Theforce trajectory 302 may be an intended force output to be provided bythe reluctance actuator 312, or a signal or information from which thesystems 300 can infer the intended force output. The force trajectory302 may be a single value of a force, such as to be provided at onetime, or a sequence or waveform of force for the intended force outputto be provided by the reluctance actuator 312 over a time interval. Theforce trajectory 302 may be produced by processors or other electronicprocessing components (not shown) of an electronic device. The forcetrajectory 302 may be intended to provide a haptic output as a responseto a user input to the electronic device.

The example systems 300 may use the force trajectory 302 as an input toa correlator component 304 to determine and provide a value or values ofan input parameter. In the specific example systems 300 shown, thecorrelator component is implemented as a look up table (LUT) 304, but adifferent implementation of the correlator component may be used. Such aprovided input parameter may be an electronic parameter value, to beused by other components of the systems 300. The input parameter orelectronic parameter value may be a current value (I), voltage value,magnetic flux value (Φ), resistance, inductance or another parametervalue to be applied to, or provided by, the reluctance actuator 312.Such an input parameter or electronic parameter value may be in the formof an analog or digital signal to be used as by other components of thesystems 300 to produce an actual output force 315.

In the embodiment shown, the LUT 304 may also contain, or be providedwith, a value L for the inductance of the reluctance actuator 312 aspart of determining the input parameter. In such embodiments, the LUT304 may be configured as a 2-dimensional array. In the embodiment shown,the determined input parameter may be one of the electrical parametervalues of current (I) or magnetic flux (Φ). Other embodiments maydetermine a different electrical parameter value from the LUT 304 usinga stored inductance value of the reluctance actuator and the given forcetrajectory 302.

Certain embodiments of the systems 300 may include any combination ofthe feed-forward component 306, the controller element 308, and themagnetic flux feedback component 320. Still other embodiments of thesystems 300 may not use any of these three components.

The input parameter may be applied as an input to the controller element308, which may be based on proportional control, and may not usefeedback, or may be a proportional/integral/derivative (PID) controllerthat accepts a feedback signal from the magnetic flux feedback component320. The input parameter may be applied as an input to a feed-forwardcomponent 306, which may convert or condition the input parameter to aform to apply to a driver component 310 that causes actuation of thereluctance actuator 312. The output signal of the feed-forward component306 may be combined with the output signal of the controller element 308to apply to the driver component 310 that causes actuation of thereluctance actuator 312. The combination of the output signals may beadditive (as shown) or subtractive, or another combination.

The driver component 310 may use the input signal to determine acorresponding output signal to apply to the reluctance actuator 312. Insome embodiments, the driver component 310 is a voltage amplifier thatamplifies and/or conditions its input signal to provide an outputvoltage signal for driving the reluctance actuator 312 to produce anactual output force 315. In other embodiments, the driver component 310is a current amplifier that amplifies and/or conditions its input signalto provide an output current signal for driving or causing actuation ofthe reluctance actuator 312 to produce an actual output force 315.

The reluctance actuator 312 accepts a driving signal and operates tocreate an actual output force 315 corresponding to the driving signal.For example, a driving signal that is a current provided by the drivercomponent 310 can induce a force as explained above in relation to thereluctance actuator 200.

Various embodiments of the systems 300, explained in more detail below,can use various feedback mechanisms and methods to reduce differencesbetween the given force trajectory 302 (and its associated intendedforce output) and the actual output force 315. These embodiments aredesigned to avoid direct measurements of the actual output force 315,since such measurements would require the use of force sensors andassociated electronics, such as on the metallic plate 204 of thereluctance actuator 200.

The feedback mechanisms and methods may use measuring or monitoring acurrent 314 a and/or a voltage 314 b in the reluctance actuator 312during an actuation. The current 314 a and voltage 314 b may be sensedat the output of the driver component 310, across the electricalcontacts 212 in the reluctance actuator 200, or at another location. Insome embodiments, a magnetic flux sensor may be included to measuredirectly a magnetic flux, such as that produced by the electromagnet 210of FIG. 2A. The measurements of any or all of the current 314 a, thevoltage 314 b, and the magnetic flux may be used as inputs for feedback.

One feedback component is the resistance and/or inductance (R/L)estimation component 316. The R/L estimation component 316 can use oneor both of the current 314 a and the voltage 314 b to obtain an estimateof a resistance R and an inductance L of the reluctance actuator 312.The resistance R may be estimated as the ratio of the voltage 314 b tothe current 314 a, though other estimation methods to obtain R may beused. The inductance L may be estimated, in embodiments in which thecurrent 314 a is an alternating current, by a phase difference betweenthe current 314 a and the voltage 314 b. Other methods for estimating Lmay be used.

The output(s) 317 of the R/L estimation component 316 may be used asinputs to a run time controller component 318. The run time controllercomponent 318 may adapt the output(s) 317 to provide a real-timefeedback to any of the feed-forward component 306, the controllerelement 308, and the magnetic flux feedback component 320. Each of thesethree components may produce their respective outputs based on presentor stored estimates of the resistance R or the inductance L of thereluctance actuator 312. As manufacturing variations, or drifts due tousage, in R and/or L may occur, the outputs of the R/L estimationcomponent 316 may be used to update those stored estimates.

The R/L estimation component 316 may provide an output 319 to the LUT304. In some embodiments, the output 319 is an estimated value of theinductance L of the reluctance actuator 312. The output 319 may be usedto update one or more inductance values in the LUT 304. The update maybe done in a quasi-static mode, in which the update is performed afterthe actuation.

The systems 300 may include a magnetic flux feedback component 320, thatmay use one or both of the measured current 314 a and the measuredvoltage 314 b to estimate a magnetic flux produced in the reluctanceactuator 312. The magnetic flux feedback component 320 may additionallyor alternatively receive a measurement from a magnetic flux sensor thatmay be included as part of the reluctance actuator 312. The magneticflux feedback component 320 may use a magnetic flux estimator 320 b thatindirectly estimates a magnetic flux based on the current 314 a and thevoltage 314 b. Additionally and/or alternatively, the magnetic fluxfeedback component 320 may use a magnetic flux state observer 320 a thatmay use a measurement of the magnetic flux in the reluctance actuator312 obtained from a magnetic flux sensor. The output of the magneticflux feedback component 320 may be provided to the controller element308 as an additional input for it to use to determine the value toprovide to the driver component 310.

As stated previously, particular embodiments of the systems 300 may useonly certain parts of the components just described. Also, othercomponents not shown in FIG. 3 may also be used, such as power supplycomponents, signal buffers, analog-to-digital converters, or othercomponents. Particular embodiments will now be described.

FIG. 4 is a block diagram of a system 400 for controlling the outputforce 315 applied by the reluctance actuator 312. The system 400 isbased on the system 300 and is directed to providing primarilyquasi-static, or non-real-time, feedback for control, with an option forreal-time control. The reluctance actuator 312 may be as described abovein relation to FIG. 3.

The system 400 is configured to receive a force trajectory 302, asdescribed above. The force trajectory 302 is used with a correlatorcomponent 404, which, in the specific example shown is the look up table(LUT) 404. In other embodiments of the system 400, another form ofcorrelator component may be used. The LUT 404 may be a 2-dimensionalarray that uses as inputs both the force trajectory 302 with a storedestimate of inductance of the reluctance actuator 312. The system 400uses the force trajectory 302 with a stored estimate of inductance ofthe reluctance actuator 312 to obtain an input parameter 405 to beapplied or read by the feed-forward component 406. In the system 400,the input parameter 405 is an electrical parameter value. In the caseshown, it is a current value. This current value may be a value forcurrent that the reluctance actuator 312 is to use during an actuation,or may be a value related to such a current (such as a digitalrepresentation thereof).

In the system 400, the feed-forward component 406 may use the inputparameter 405 to determine an input voltage value to apply to thevoltage amplifier 408. The voltage amplifier 408 may buffer or amplifythe input voltage value applied to produce the output drive value 409 ofa voltage needed to drive the reluctance actuator 312 into actuation.

As described above, the current 314 a and the voltage 314 b of thereluctance actuator 312 may be measured or monitored during theactuation. The measured values of the current 314 a and the voltage 314b may be used by the R/L estimation component 316, as described above,to obtain one or both of an estimate of the resistance R and of theinductance L of the reluctance actuator 312.

In one embodiment, one or both of the estimates of the resistance andthe inductance may then be used as feedback values to adjust operationof the feed-forward component 406. As an example, the estimatedresistance value R may be used to determine how the output voltage 407is determined from the input parameter 405. The adjustment may be madein real-time, such as during a time interval in which the voltageamplifier 408 is driving the reluctance actuator 312. Additionallyand/or alternatively, the adjustment may be a quasi-static control, toadjust internal memory or parameters used by the feed-forward component406 after the actuation.

In another embodiment, the estimated value of the inductance 319 may beused to adjust the LUT 404. This adjustment may be made as aquasi-static method of control after the actuation.

FIG. 5 is a block diagram of a system 500 for controlling the outputforce 315 applied by a reluctance actuator 312. The system 500 is basedon the general system 300 of FIG. 3, and is directed to providingquasi-static, or non-real-time, feedback for control.

The system 500 is configured to receive a force trajectory 302, such asdescribed above. The force trajectory 302 is used with the correlatorcomponent 504, which, in the specific example shown, is the look uptable (LUT) 504. In other embodiments of the system 500, another form ofcorrelator component may be used. The LUT 504 may be a 2-dimensionalarray that uses as inputs both the force trajectory 302 with a storedestimate of inductance of the reluctance actuator 312. The system 500uses the force trajectory 302 with a stored estimate of the inductanceof the reluctance actuator 312 to obtain an input parameter 505 to beapplied or read by the current mode amplifier 506. In the system 500,the input parameter 505 is an electrical parameter value; in the caseshown it is an input current value 505. This current value may be avalue for current that the reluctance actuator 312 is to use during anactuation, or may be a value related to such a current (such as adigital representation thereof).

In the system 500, the current mode amplifier 506 may use the inputcurrent value 505 to determine an output drive value 507 of a currentwith which to drive the reluctance actuator 312 into actuation.

As described above, the current 314 a and the voltage 314 b of thereluctance actuator 312 may be measured or monitored during theactuation. The measured values of the current 314 a and the voltage 314b may be used by the R/L estimation component 316, as described above,to an estimate 319 of the inductance L of the reluctance actuator 312.That estimate may then be used to adjust the LUT 504. This adjustmentmay be made as a quasi-static method of control.

FIG. 6 is a block diagram of a system 600 for controlling the outputforce 315 applied by a reluctance actuator 312. The system 600 is basedon the general system 300 of FIG. 3, and is directed to providingreal-time feedback for control.

The system 600 is configured to receive a force trajectory 302, such asdescribed above. The force trajectory 302 is used with a correlatorcomponent 604, which, in the specific example shown, is the look uptable (LUT) 604. In other embodiments of the system 600, another form ofcorrelator component may be used. The LUT 604 may be a 2-dimensionalarray that uses as inputs both the force trajectory 302 with a storedestimate of inductance of the reluctance actuator 312. The system 600uses the force trajectory 302 with a stored estimate of the inductanceof the reluctance actuator 312 to obtain an input parameter 605 a to beapplied or read as a first input by the controller element 608. Theinput parameter 605 a may also be applied or read as an input to thefeed-forward component 606. In the specific embodiment of FIG. 6, theinput parameter 605 a is an input current value (I), which may be acurrent value to be applied by the reluctance actuator 312 during anactuation, or may be a value related to such a current (such as adigital representation thereof).

The feed-forward component 606 of the system 600 may use the inputparameter 605 a to determine a first driver input value 607 a. In theembodiment shown, the feed-forward component 606 produces a voltagevalue as the first driver input value 607 a to be used by the drivercomponent 610, which may be a voltage driver for the reluctance actuator312. In other embodiments, the first driver input value 607 a producedby the feed-forward component 606 may instead be a current value to beused in the case that the driver component 610 is a current driver forthe reluctance actuator 312.

The controller element 608 of the system 600 may be based onproportional control, and may not use feedback, or may be aproportional/integral/derivative (PID) controller that accepts afeedback signal 605 b. In the embodiment shown, the feedback signal 605b, is a current feedback signal, described further below. In theembodiments in which the controller element 608 accepts a feedbacksignal 605 b, the input parameter 605 a and the feedback signal 605 bmay be combined, either by differencing or additively, to produce acontroller input signal 605 c that is used by the controller element608.

The controller element 608 may use the controller input signal 605 c todetermine a second driver input value 607 b. In the embodiment shown,the controller element 608 produces a voltage value as the second driverinput value 607 b to be used by the driver component 610, which may be avoltage driver for the reluctance actuator 312. The first driver inputvalue 607 a and the second driver input value 607 b may be combined(such as additively, averaging, or another method) to produce thecombined driver input 607 c applied to the driver component 610. Thedriver component 610 may then apply a corresponding output drive valueor signal 611 to the reluctance actuator 312 to cause its actuation. Theoutput drive value 611 may be a single constant value, or a time-varyingsignal.

As described above, the current 314 a and the voltage 314 b of thereluctance actuator 312 may be measured or monitored during theactuation. The measured values of the current 314 a and the voltage 314b may be used by the R/L estimation component 316, as described above,to produce estimates 317 of the resistance R and of the inductance L ofthe reluctance actuator 312.

The estimate of the inductance L 319 of the reluctance actuator 312 maythen be used to adjust the LUT 604. This adjustment may be made as aquasi-static method of control, such as by adjusting the LUT 604 afterthe actuation.

In some embodiments of the system 600, the estimates 317 of theresistance R and of the inductance L of the reluctance actuator 312 maybe used to adjust operation of the feed-forward component 606 and/or thecontroller element 608.

The system 600 may use real-time feedback control, in which the measuredvalue of at least one of the current 314 a and the voltage 314 b of thereluctance actuator 312 during the actuation is applied as the feedbacksignal 605 b used by the controller element 608. If the actuation is ofsufficient duration in time, the real-time feedback control may alterthe current 314 a and the voltage 314 b of the reluctance actuator 312during the actuation. The R/L estimation component 316 may use onlyvalues of the current 314 a and the voltage 314 b that occur at or nearthe end of the actuation to obtain the estimate of the inductance L 319used to adjust the LUT 604.

FIG. 7 is a block diagram of haptic output device 700 that includesvarious control electronic components to control an output force 315applied by the reluctance actuator 312. The reluctance actuator 312 maybe as described above, and may be configured with an electromagnet toinduce movement of a metallic plate that is transferred as a hapticoutput to a surface of an electronic device that includes the hapticoutput device 700. The haptic output device 700 is configured to usereal-time feedback control based on estimating the magnetic flux in thereluctance actuator 312. The estimates of the magnetic flux in thereluctance actuator 312 in turn may be based on monitored values of acurrent 314 a and/or a voltage 314 b across the reluctance actuator. Thehaptic output device 700 is also configured to use quasi-static feedbackcontrol, also based on monitored values of the current 314 a and/or thevoltage 314 b across the reluctance actuator 312.

The control electronic components of the haptic output device 700 areconfigured to receive an intended force output or force trajectory 302from a processor or other component of the electronic device. In theembodiment shown, the force trajectory 302 may be received by acorrelator component 704 that may either be implemented as, or include,a LUT. The correlator component 704 may include a memory, which may bepart of the LUT itself, and that includes one or more stored estimatesof an inductance (L) of the reluctance actuator 312. A received forcetrajectory 302 and the stored estimates of the inductance may be used bythe correlator component 704 to provide the input parameter 705 a. Inthe embodiment shown, the input parameter 705 a is an expected magneticflux value (Φ) to occur in the reluctance actuator 312.

The haptic output device 700 may include a controller element 706 thatuses the expected magnetic flux 705 a as a first input. The controllerelement 706 of the haptic output device 700 may be based solely onproportional control and not use feedback, or may be aproportional/integral/derivative (PID) controller that accepts afeedback signal 705 b. In the embodiment shown, the feedback signal 705b is an estimated value of the magnetic flux, as described furtherbelow. The expected magnetic flux 705 a and the feedback signal 705 bmay be combined (by differencing, averaging, or another method) toproduce the controller input signal 705 c used by the controller element706.

The controller element 706 may provide a driver input value 707 that isused by the driver component 710. The driver component 710 may be acurrent amplifier or other current based driver, and the driver inputvalue 707 may then be a current value. In alternative embodiments, thedriver component 710 may be a voltage amplifier or other voltage baseddriver, and the driver input value 707 may then be a voltage value. Thedriver component 710 causes the reluctance actuator 312 to actuate andproduce the actual output force 315 that is transmitted to a surface ofthe electronic device containing the haptic output device 700.

As described above, the current 314 a and the voltage 314 b of thereluctance actuator 312 may be measured or monitored during theactuation. The measured values of the current 314 a and the voltage 314b may be used by the R/L estimation component 316, as described above,to produce estimates 317 of the resistance R and the inductance L of thereluctance actuator 312. The estimate 319 of the inductance L of thereluctance actuator 312 may then be used to adjust the LUT in thecorrelator component 704. This adjustment may be made as a quasi-staticmethod of control, such as by adjusting the LUT within the correlatorcomponent 704 after the actuation.

The haptic output device 700 may use real-time feedback control as wellas, or as an alternative to, the quasi-static method of control, inwhich the measured value of at least one of the current 314 a and thevoltage 314 b of the reluctance actuator 312 during the actuation are bya flux estimator 708 to produce the feedback signal 705 b. The feedbacksignal 705 b may be an estimate of the magnetic flux produced in thereluctance actuator 312 during its actuation. The flux estimator 708 mayalso use the estimates 317 of the resistance R and of the inductance Lof the reluctance actuator 312 to produce the estimate of the magneticflux. The estimate of the magnetic flux may use parameters of thereluctance actuator known from manufacture, such as the cross-sectionalarea and number of windings.

In other embodiments, the feedback signal 705 b giving the estimate ofthe magnetic flux may be provided directly by a magnetic flux sensor,such a Hall sensor, positioned near or in the reluctance actuator 312.Additionally and/or alternatively, a gap distance sensor may be includedin the reluctance actuator 312 to provide a measurement of the gapbetween the metallic plate and the electromagnet of the reluctanceactuator 312.

FIG. 8 is a block diagram of a method 800 for control of a force appliedby a reluctance actuator, such as the reluctance actuator 200 of FIGS.2A-B. The method 800 may be applied by an electronic device having theconfigurations of components and reluctance actuators as describedpreviously, such as in relation to the embodiments of FIGS. 3-7.

At stage 802 a force trajectory or intended force output is received,such as by a control system or other electronic components controllingoperation of a reluctance actuator. The intended force output may beprovided to such a control system or components from a processor oranother source, and may be based on an input received by the electronicdevice (such as a user input on a touch screen or other input mechanism)or on a state of the electronic device (such as an alarm timeoccurring). The intended force output may be different for differentinputs to, or states of, the electronic device.

At stage 804, the method 800 uses the intended force output as at leastone input value to use with a correlator component, which may beimplemented as a look up table (LUT). Though for simplicity thecorrelator component is described as a LUT, another implementation of acorrelator component may be used. The LUT may be implemented as atwo-dimensional array, needing two supplied selection input values toselect or produce a single output. The LUT may use the received intendedforce output and a stored estimated value of an electronic parameter ofthe reluctance actuator. In some embodiments the stored estimated valuemay be an estimated value of the inductance of the reluctance actuator.

In other embodiments, the LUT may be implemented as a three- (or higher)dimensional array, needing the intended force output together with two(or more) stored estimates of electrical parameter values of thereluctance actuator. For example, a three-dimensional LUT may take in anintended force output, a value for an inductance of the reluctanceactuator, and a value of a resistance of the reluctance actuator.

At stage 804, the method 800 obtains an input parameter from the LUT,which may be a current, voltage, or magnetic flux signal, to use withelectronic components that cause actuation of the reluctance actuator,such as an amplifier (e.g., voltage or current) or other form ofactuator driver. The value of the input parameter from the LUT may be ina digital format that is read by the electronic components and used toproduce an analog signal (e.g., voltage or current) that actuates thereluctance actuator.

At stage 806, the value of the input parameter determined using the LUTis used by the electronic components that cause actuation of thereluctance actuator. The electronic components that cause actuation mayalso receive and use other input values, such as a value of magneticflux being produced by the reluctance actuator, as part of actuating thereluctance actuator. As another example, the electronic components mayreceive a current limit value that prevents them from applying too largea current to the reluctance actuator. Such a current limit value mayvary over time, based on a temperature of the electronic device or on aremaining charge in a battery.

At stage 808, the method measures or monitors the voltage and/or currentthrough the reluctance actuator. Based on the values of the voltageand/or current, parameters of the reluctance actuator are estimated.These parameters may be estimates for the force produced by thereluctance actuator during the actuation, an inductance and/orresistance of the reluctance actuator, or another parameter.

At stage 810, the LUT can be updated if it is found, for example, that ameasured or inferred force output produced by the reluctance actuatordiffers from the received force trajectory or intended force output, andwhat was expected based on the input parameter obtained in stage 804.The LUT may also be updated if an estimated value of an inductance orresistance of the reluctance actuator, based on the measured voltageand/or current during the actuation, differs from respective valuesstored in the LUT.

The updated LUT may then be used with a subsequently received inputforce trajectory to improve accuracy of a subsequent force output by thereluctance actuator.

FIG. 9 is a flow chart of a method 900 for control of a force applied bya reluctance actuator. The method 900 may be applied by an electronicdevice having certain of the configurations of components and reluctanceactuators as described previously in relation to FIGS. 3, 6, and 7 toimplement real-time control of a force output by a reluctance actuator.The method 900 also may include actions to implement quasi-staticcontrol of the force output.

At stage 902, a force trajectory or intended force output is received,such as by a control system or other electronic components controllingoperation of a reluctance actuator. The intended force output may beprovided to such a control system or components from a processor oranother source, and may be based on an input received by the electronicdevice (such as a user input on a touch screen or other input mechanism)or on a state of the electronic device (such as an alarm timeoccurring). The intended force output may be different for differentinputs to, or states of, the electronic device.

At stage 904, the method 900 uses the intended force output as at leastone input value to use with a correlator component, which may beimplemented as a look up table (LUT). Though for simplicity thecorrelator component is described as a LUT, another implementation of acorrelator component may be used. The LUT may be implemented as atwo-dimensional array, needing two supplied input values or parametersto select or produce a single output. The LUT may use the receivedintended force output and a stored estimate of an electronic parametervalue of the reluctance actuator. In some embodiments the storedestimate may be an estimated value of the inductance of the reluctanceactuator. As discussed previously, the LUT may be a three- or evenhigher dimensional, depending on the number quantities needed to look upa corresponding output value.

At stage 904, the method 900 also obtains an input parameter from theLUT, which may be a current, voltage, or magnetic flux signal, to usewith electronic components that cause actuation of the reluctanceactuator, such as an amplifier (e.g., voltage or current) or other formof actuator driver. The value of the input parameter from the LUT may bein a digital format that is read by the electronic components and usedto produce an analog signal (e.g., voltage or current) that actuates thereluctance actuator.

At stage 906, the input parameter obtained from the LUT is received as afirst input to a controller element. The controller element may alsoreceive a feedback parameter value as its second input. The feedbackparameter may be a current, such as current 314 a, or may be a voltage,such as voltage 314 b, as described above. The controller element canuse the two inputs separately, or as a combination, to determine acontroller output value to be applied to a driver component of thereluctance actuator.

At stage 908, the controller output value is applied by the drivercomponent to actuate the reluctance actuator. The controller outputvalue may be a current value, a voltage value, or another parametervalue.

At stage 910, parameter values of the reluctance actuator may beestimated based on operational measurements of the reluctance actuatorduring the actuation. Such parameter values may include an inductance, aresistance, internal capacitances, and the like. The operationalmeasurements may be of a current, a voltage, a magnetic flux in or nearthe reluctance actuator, or another operational measurement.

The estimated parameter values of the reluctance actuator can then beused as feedback, either for quasi-static or real-time feedback. One ormore of the determined parameter values may be used by the controllerelement as part of real-time feedback control of the reluctanceactuator's output force, as indicated by the solid feedback line.

Additionally and/or alternatively, one or more determined parametervalues of the reluctance actuator, such as an inductance, may be used toupdate the LUT. Such an update may be performed after the actuation toimplement quasi-static control.

In some embodiments of stage 910, additional operational measurements ofthe reluctance actuator may be obtained using sensors that do notdirectly measure the output force applied by the reluctance actuator.These additional operational measurements may include a measurement of agap between a metallic plate and an electromagnet of the reluctanceactuator. At stage 912, during the actuation the gap measurement may bemade, such as by a capacitive or another type of sensor. The additionaloperational measurements may further include a measurement of a magneticflux within the reluctance actuator. At stage 914, during the actuationthe magnetic flux may be measured, such as by a Hall sensor mounted onthe metallic plate. The magnetic flux sensor may be positioned on themetallic plate above the axis of the windings of the electromagnet.

Other examples and implementations are within the scope and spirit ofthe disclosure and appended claims. For example, features implementingfunctions may also be physically located at various positions, includingbeing distributed such that portions of functions are implemented atdifferent physical locations. Also, as used herein, including in theclaims, “or” as used in a list of items prefaced by “at least one of”indicates a disjunctive list such that, for example, a list of “at leastone of A, B, or C” means A or B or C or AB or AC or BC or ABC (i.e., Aand B and C). Further, the term “exemplary” does not mean that thedescribed example is preferred or better than other examples.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of the specificembodiments described herein are presented for purposes of illustrationand description. They are not targeted to be exhaustive or to limit theembodiments to the precise forms disclosed. It will be apparent to oneof ordinary skill in the art that many modifications and variations arepossible in view of the above teachings.

What is claimed is:
 1. A method of controlling a force applied by areluctance actuator, comprising: receiving an intended force output tobe applied by the reluctance actuator; obtaining from a correlatorcomponent, based at least on the intended force output and a storedestimate of an electrical parameter value of the reluctance actuator, aninput parameter to be applied to the reluctance actuator; actuating thereluctance actuator by applying the input parameter to the reluctanceactuator to cause an actuation of the reluctance actuator; obtaining atleast one of a measurement of a current or a measurement of a voltage inthe reluctance actuator during the actuation; estimating the electricalparameter value of the reluctance actuator using the at least one of themeasurement of the current or the measurement of the voltage; andupdating the stored estimate of the electrical parameter value of thereluctance actuator based on the estimation of the electrical parametervalue of the reluctance actuator.
 2. The method of claim 1, wherein theinput parameter is at least one of a current applied by a current driverto the reluctance actuator or a voltage applied by a voltage driver tothe reluctance actuator.
 3. The method of claim 1, wherein: thecorrelator component is look up table (LUT); and the electricalparameter value of the reluctance actuator is an inductance of thereluctance actuator.
 4. The method of claim 3, wherein updating thestored estimate of the inductance of the LUT occurs after the actuation.5. The method of claim 1, further comprising obtaining, from a magneticflux sensor, a measurement of the magnetic flux produced by thereluctance actuator.
 6. The method of claim 5, wherein the measurementof the magnetic flux is used with the at least one of the measurement ofthe current or the measurement of the voltage to perform the operationof estimating an actual inductance of the reluctance actuator.
 7. Ahaptic actuator comprising: a reluctance actuator including: a metallicplate; and an electromagnet positioned adjacent to the metallic plate;and control electronic components including: a correlator component; adriver component operably linked with the electromagnet; and anestimation component; wherein the control electronic components areoperable to: receive a force trajectory; determine an input parameterfor the driver component using the force trajectory with the correlatorcomponent; apply the input parameter to the driver component to cause anactuation of the reluctance actuator; monitor, by the estimationcomponent, a voltage and a current in the reluctance actuator during theactuation; and update the correlator component based on the monitoredvoltage and the monitored current in the reluctance actuator during theactuation.
 8. The haptic actuator of claim 7, wherein: the correlatorcomponent contains a memory implementing a look up table (LUT); the LUTincludes a stored estimate of an inductance of the reluctance actuator;and the stored estimate of the inductance of the reluctance actuator isused with the force trajectory to determine the input parameter for thedriver component.
 9. The haptic actuator of claim 8, wherein updatingthe LUT includes updating the stored estimate of the inductance of thereluctance actuator.
 10. The haptic actuator of claim 7, wherein: thedriver component is a current amplifier; and the input parameter is aninput current.
 11. The haptic actuator of claim 7, wherein: the drivercomponent is a voltage amplifier; and the input parameter is an inputvoltage.
 12. The haptic actuator of claim 7, wherein: the controlelectronic components further comprise a controller element; thecontroller element is configured to provide a feedback control input tothe driver component; and the feedback control input is at leastpartially based on the monitored current value.
 13. The haptic actuatorof claim 12, wherein the control electronic components further include amagnetic flux estimator operable to: determine an estimate of a magneticflux in the reluctance actuator during the actuation based on themonitored voltage value and the monitored current value in thereluctance actuator; and provide the estimate of the magnetic flux inthe reluctance actuator to the controller element.
 14. The hapticactuator of claim 13, wherein the control electronic components furtherinclude a magnetic flux sensor associated with the electromagnet andoperable to: obtain a measurement of the magnetic flux in the reluctanceactuator during the actuation; and provide the measurement of themagnetic flux to the magnetic flux estimator.
 15. A method of control ofa force applied by a reluctance actuator that includes an electromagnetand a flexible metallic plate, comprising: receiving an intended forceoutput; obtaining from a correlator component, based on the intendedforce output and a stored value of an electrical parameter value of thereluctance actuator, an input parameter; receiving, at a feedbackcontroller, the input parameter and a feedback value of the electricalparameter value of the reluctance actuator; applying, by the feedbackcontroller, an input drive value to a driver component, the input drivevalue based on the input parameter and the feedback value of theelectrical parameter value of the reluctance actuator; applying, by thedriver component, an output drive value to the electromagnet to actuatethe reluctance actuator; measuring a current in the reluctance actuatorduring the actuation; and using the measurement of the current in thereluctance actuator during the actuation to determine the feedback valueof the electrical parameter value of the reluctance actuator.
 16. Themethod of claim 15, wherein: the correlator component is a look up table(LUT); the stored value of the electrical parameter value of thereluctance actuator is an initial value of an inductance; and the inputparameter is a current value.
 17. The method of claim 16, wherein: theinput drive value is a first input drive value; and the method furthercomprises: determining, based on the input parameter, a second inputdrive value; and applying, by a feed-forward component, the second inputdrive value to the driver component.
 18. The method of claim 16, furthercomprising: measuring a voltage in the reluctance actuator during theactuation; determining an estimated resistance and an estimatedinductance of the reluctance actuator based on the measured current andthe measured voltage in the reluctance actuator during the actuation;and updating the LUT by replacing the initial value of the inductance ofthe reluctance actuator with the estimated inductance of the reluctanceactuator.
 19. The method of claim 18, wherein the input parameter is aninput value of a magnetic flux, and the method further comprises:estimating a magnetic flux in the reluctance actuator during theactuation based on the measured current and the measured voltage in thereluctance actuator during the actuation; and using the estimatedmagnetic flux in the reluctance actuator as the feedback value of theelectrical parameter value received at the feedback controller.
 20. Themethod of claim 16, wherein the input parameter is an input value of amagnetic flux, and the method further comprises: receiving, from amagnetic flux sensor associated with the electromagnet, a measurement ofa magnetic flux in the reluctance actuator during the actuation; andusing the measurement of the magnetic flux in the reluctance actuatorduring the actuation as the feedback value of the electrical parametervalue received at the feedback controller.